1. Field of the Invention
The present invention relates to a method of manufacturing an optical sensor, an optical sensor, and a camera.
2. Description of the Related Art
A solid-state image pickup device, which serves as an optical sensor for an image pickup apparatus, is known. In an optical sensor based on solid-state technology, an image pickup device chip obtained by dividing a wafer into individual chips is encapsulated in a cover member by using a plastic package or a ceramic package having a depression. In such an optical sensor, it is known that, when a glass is used as the cover member, α rays emitted from heavy metals or the like included in the glass adversely affect characteristics of the image pickup device chip. Therefore, a configuration in which a crystal that emits no α rays has been proposed to be used as the cover member of the optical sensor (see Japanese Patent Application Laid-Open No. 2008-34502). Further, a configuration in which a glass that emits small amounts of α rays has also been proposed to be used as the cover member (see Japanese Patent Application Laid-Open No. 05-279074).
WLCSP (wafer level chip size package) is known which is obtained by fixing a wafer-state semiconductor substrate including image pickup devices and a light transmissive substrate together and dividing the fixed substrates into individual chips. A configuration and a manufacturing method of the WLCSP are disclosed, for example, in Japanese Patent Application Laid-Open No. 2010-050260. WLCSP-type optical sensors can be processed collectively at the wafer level, so that the manufacturing cost can be reduced, and a small and thin optical sensor can be realized.
However, when a light transmissive substrate formed of a crystal that emits no α rays or a glass that emits small amounts of α rays is fixed to a wafer, there is a problem that warping of the wafer or light trasmissive substrate or both occurs due to thermal expansion during a manufacturing process and the yield rate decreases. In addition, even after manufacturing, there is a problem that a crack or peeling occurs if warping takes place between the fixed light transmissive substrate and the wafer. Therefore, an optical sensor obtained by dividing the fixed substrate and wafer into individual chips has the same problem.
The present invention provides a manufacturing method of an optical sensor in which influence of α rays to the image pickup device chip can be reduced and warping can be suppressed. Accordingly, the optical sensor, and a camera using the optical sensor can be made more reliable.